1. Field of the Invention
The present invention relates to a stereoscopic retinal camera, and more particularly relates to a mechanism to amend a fluctuation of a stereoscopic visual angle or an inter-image pitch or the like which is caused by a difference of a portion to be photographed or a refracting power of an examinee's eye.
2. Description of Related Art
A conventional optical system of a stereoscopic retinal camera is as shown in FIG. 7. The construction of the optical system is similar to the system of the embodiment of the present invention which will be mentioned later. In the apparatus of FIG. 7, the light beam reflected by the fundus of an examinee's eye 14 is focused at point A in an inverted image by an objective lens 13, and passing through an aperture of a perforated mirror 12, the light beam is split into two light beams by a two-hole diaphragm 15. The separated light beam is interchanged to a right light beam and a left light beam, the image distance is extended. If there is a defective sight ametropy in the examinee's eye, the photographer moves a focusing lens 19 to a direction of the optical path, so that the fundus image of the eye i s formed on a film 21. In the case of normal eye, the position of the first intermediate image at point A is moved to A.sup.- side direction along with the optical axis on nearsight, and moved to opposite A.sup.+ side direction on farsight. Therefore, the inter-image pitch on a field stop 27 and a film 21 is changed, whereby a stereoscopic visual angle is changed. This changing is extremely inconvenient for prosecuting a stereoscopic measurement precisely.
Further, there is provided an apparatus which is able to photograph not only eye's fundus, but also a front portion of the eye, in general retinal cameras. Such a kind of apparatus comprises a convex auxiliary lens which is disposed in the photographing optical system insertably. If this kind of mechanism for photographing the front of the eye is adopted on the stereoscopic retinal camera, the stereoscopic visual angle is changed largely, and the inter-image pitch is also changed to small size P' within a range of size P, shown in FIG. 2.
Accordingly, the synthesized area as a stereoscopic image becomes narrow, and a problem is caused in the direct vision of the stereoscopic image.